A variety of mixing devices are used in industry. For example, certain mixers are used in operation with flue-gas desulfurization (“FGD”) units, which are commonly used in the electric power generation industry to remove sulfur dioxide from flue-gas, where flue-gas is a byproduct of coal-fired electric power generation. It is desirable to remove the sulfur dioxide for pollution abatement purposes and because sulfur dioxide can be used to make a number of safe and useful products, such as gypsum.
Typically, FGD units include a large vessel in which slurry is stowed and mixed. The slurry, for example, may be a mixture of water and limestone. The slurry is mixed for the purpose of suspending the limestone in the slurry and to prevent the slurry from hardening and settling at the bottom of the vessel. Oftentimes, multiple mixing devices are employed at the same time to effectuate mixing within a single vessel, where each mixing device includes a drive that is mounted on the outside of the vessel and a horizontal impeller shaft that extends from the drive to the inside of the vessel. For example, the drive may be mounted to a bearing housing that is mounted on an outside-wall of the vessel, and the impeller shaft may be rotatably driven by the drive. Radially extending impellers are located at one or several locations on the length of the impeller shaft. The impellers have paddles or blade type features along some or all of their length and which mix the slurry inside the vessel.
In some instances, these mixing devices include a mechanical seal located between the impeller shaft and an opening formed in a sidewall of the vessel. The mechanical seal is configured to allow the impeller shaft to pass into the vessel by way of the aforementioned opening, yet prevent the contents of the vessel from escaping by way of the opening. It is typically desirable to provide such a seal so that the slurry does not flow in the bearing housing and come in contact with moving parts, such as bearings and gears. Periodically, the mechanical seal wears to the extent that it loses its effectiveness and needs to be replaced.
When the drive is mounted to the bearing housing, there is no access to the mechanical seal. A known way to provide access to the seal for replacement, is to disconnect and remove the drive and its associated parts from the end of the bearing housing. Removal of the drive creates a gap or access opening in the bearing housing where the drive was once mounted. This access opening provides a passageway through which the seal can be accessed and handled. For example, a mechanic can reach through the access opening and into the bearing housing where he can disconnect the seal. Once the seal is disconnected, the mechanic can then slide the seal off impeller shaft and then remove the seal via the access opening. However, this arrangement is disadvantageous because before the drive can be removed, an electrician must disconnect the drive leads and a millwright must remove the drive, both of which are time consuming and potentially expensive processes. The drive, including the motor, can be very heavy. Therefore, once the drive leads and drive have been removed, an overhead crane, or the like, is used to support the drive while it is disengaged from the bearing housing.
Another known way to provide an access opening through which the seal can be accessed and replaced is to provide a long bearing housing having a large side-opening located proximate to the seal. A spool piece is used to connect the impeller shaft to the drive output shaft. The spool piece is removable so that when it is removed, a gap is created between the impeller shaft and the drive output shaft. The spool piece is wide enough to leave a gap wide enough to permit at least a portion of the mechanical seal to pass therethrough. This arrangement is disadvantageous because it requires that the mechanic work adjacently beside the seal instead of directly behind the seal. Because the mechanic is forced to work beside the seal, the seal is difficult to access and handle. For example, the mechanic must reach across the impeller shaft and the entire face of the seal, and because the seal is large and heavy, it is difficult for a mechanic to dismount the seal from the impeller shaft, through the gap created by the spool, and through the side-opening.
Accordingly, it is desirable to provide a method and apparatus which can mount and dismount a drive system and alleviate the above mentioned disadvantages at least to some extent, and which can in some embodiments provide a mixer drive connection and also allow access via an access opening through which the mechanical seal can be easily handled and replaced.